1. Field of the Invention
The present invention relates to a coating apparatus for coating a coating liquid such as a resist liquid onto a surface of an object to be treated such as a semiconductor wafer or the like.
2. Description of the Related Art
In the photolithography step for instance, in the manufacturing process of a semiconductor device, for instance, the resist coating treatment for forming a resist film on a surface of a semiconductor wafer (hereinafter refers to as xe2x80x9cwaferxe2x80x9d) is carried out, after an exposing treatment is carried out to the wafer thereon the resist is coated, a developing treatment is carried out.
FIG. 22 is a diagram showing diagrammatically a constitution of a resist liquid supply system of a conventional resist coating apparatus.
When an attention is paid to a device for coating a resist, in the conventional coating apparatus, as shown in FIG. 22, a resist liquid stored in a resist tank 201 is pumped out by a supplying pump 202 and stored in a buffer tank 203 once, then the resist liquid stored in the buffer tank 203 is sent by pressure towards a nozzle 205 by a discharging pump 204, and by switching the flowing course of the resist liquid by a valve 206 disposed between the discharging pump 204 and the nozzle 205, the timing of discharge of the resist liquid from the nozzle 205 is controlled.
The valve 206 employed here is an air operation valve which is driven through a compressed air and is provided with a structure in which the flowing courses on the sucking side and the discharging side are opened or closed therebetween by a cylinder operated by the compressed air, and switching of flowing in/stoppage of the compressed air is carried out by a solenoid valve 207 disposed between an air compressor which sends the compressed air and the valve 206. This solenoid valve 207 has a structure that the solenoid is driven based on the electrical signals from a controller 208 to open or close the flowing course of the compressed air.
Further, the switching speed of the valve 206 is controlled by a speed controller 209 disposed between the solenoid valve 207 and the valve 206. This speed controller 209 has a structure in which the width of the flowing course of the compressed air is adjusted by an amount of projection of a needle and the amount of projection of the needle is adjusted manually.
Incidentally, in order to form a resist film of excellent quality on a wafer, a predetermined amount of a resist liquid is dripped on an wafer revolving with a high speed and diffused due to a centrifugal force over the whole wafer, at the same time, the superfluous resist liquid is required to be removed from on the wafer. Therefore, rotation of the wafer, the discharging pump 204 and the valve 206 are required to be operated with the predetermined timings.
However, in the aforementioned conventional coating apparatus, there tends to occur a time lag between from the sending of the operational signal from the controller 208 up to the actual switching operation of the valve 206.
This time lag is adjusted by use of the speed controller 209. However, it varied due to the length of the flowing course or the individual difference of the valves themselves, accordingly the adjustment thereof is very difficult. Therefore, there was a problem that the timing of the discharge of the resist liquid deviated against the revolution of the wafer to induce occurrence of films of bad quality such as the films of the fluctuated thickness.
In addition, as shown in FIG. 22, in the case of the resist tank 201 being disposed below the floor, a buffer tank 203 is required to be disposed between from the resist tank 201 to the discharging tank 204. However, when the buffer tank 203 is disposed, accompanying this, a liquid level sensor 211 becomes necessary. There occur such problems that it leads to the rise of the cost or larger size of foot print, and, due to an increase of the surface area which makes a contact with the air, the resist liquid tends to deteriorate.
The present invention was made to solve such problems as described above, an objective of the present invention is to provide a coating apparatus which can make as short as possible the time lag up to operation of the valve.
Another objective of the present invention is to provide a coating apparatus in which the discharging pump and the valve can be operated with the best timings.
Still another objective of the present invention is to provide a coating apparatus in which a switching valve and a suck back valve can be operated at the best timing.
The still another objective of the present invention is to provide a coating apparatus in which the rise of the cost and deterioration of the resist liquid can be prevented from occurring.
The coating apparatus of the present invention comprises a nozzle discharging a coating liquid to an object to be treated, a container for storing the coating liquid, a discharging pump which is disposed between the nozzle and the container and sends out the coating liquid in the container to the nozzle, a speed controlling means, disposed between the discharging pump and the nozzle, of controlling electrically the switching speed, and a controlling means for controlling the operation of the discharging pump.
The aforementioned coating apparatus, in which the valve is consisting of a switching valve and a suck back valve, may be provided with a controller exclusively controlling the operation of the switching valve and the suck back valve.
Further, the aforementioned coating apparatus may be further provided with a pressure detecting means for detecting the pressure of the coating liquid on the downstream side of the discharging pump, and the controlling means may be a means which controls the operation of the valve based on the detected pressure of the coating liquid.
Further, the coating apparatus, which is disposed between the container and the discharging pump, may be further provided with a supplying pump for supplying the coating liquid in the container to the discharging pump, and a pressure controlling means for controlling the pressure of the coating liquid of the down stream side of the supplying pump, wherein the controlling means may be a means for controlling the pressure of the supplying pump based on the operation of the discharging pump.
Further, the controlling means may be a means for controlling the pressure of the supplying pump and the timing of the operation of the valve based on the actions of the discharging pump.
The aforementioned device may further comprise a means for detecting the pressure of the coating liquid of the down stream side of the discharging pump, a supplying pump, which is disposed between the container and the discharging pump, for supplying the coating liquid in the container to the discharging pump, and, a means for controlling the pressure of the coating liquid of the down stream side of the supplying pump, wherein the controlling means may be a means which, based on the pressure detected by the pressure detecting means, controls the actions of the discharging pump and the valve, and at the same time, controls the pressure of the supplying pump based on the actions of the discharging pump.